Alternating-current motor.



" Witnesses.

ps27,e19.- BATENTEDJULY 31.19 06;

' M. MILOH.

". ALTBRNATING CURRENT MOTOR.

' firmo'm'xonrnnn up. a, 1905.-

Inventor.

Maurice Milch.

I UNITED STATES PATENT orricn.

MAURicE mtcnor SCHENEGTADY, NEW YORK, ASSIGNOR TO GENERAL ELECTRICCOMPANY, A CORPORATION or NE -YOR AL TERNATlNG-CURBENT MOTOR.

' To all whom, it may concern.-

Be it known that I, MAURICE MILGH, a subject ofthe Emperor ofAustria-Hungary,residin at Schenectady, in the county of Schenecta y,State of New Y,ork, have invented certain new and useful Improvements inAlternating-Current Motors, of which the following is a specification.

My, invention relates to alternating-current motors of the commutatortype; and its object is to provide a novel arrangement of circuits andcontrolling means for such motors, whereby the motor has a largestarting torque, but when started operates only in the neighborhood ofsynchronism.

The ordinary single-phase induction-motor which, operates always in theneighbor hood of synchronism is not suitable for use in manyapplications, since it has no starting torque. Alternating-currentmotors of the commutator t e, such as repulsion and series motors, on te other hand, have a large starting tor ue With a speed-torquecharacteristic sim' ar to that of the direct-current series motor. Theyare consequently likely to race on light roads and are not suited foruse in certain applications, such as elevator work,'where the load mayat times be very small.

In two of my former applications, Serial No. 189,121, filed January 15,1904, and Serial No. 223,838, filed September 9, 1904, I have disclosedan-arrangement whereby an -alternating-current motor of the commutatortype may be started as an ordinary repulsion-motor, and then when it isup to speed a second rotor-circuit may be closed. so as to cause themotor to operate substantially at .synchronism. The switch for producingthe second short circuit may be either manual or automatic, and in myformer applications above referred to I have disclosed two types ofautomatic switches adapted for this purpose.

My present invention relates to the control of motors in which currentis supplied directly to the armature-winding at starting-such, forinstance, as the series motor and it consists in the combination, in analter Specification of Letters Patent.

Applicatibn filatl January 3,1905. Serial No. 289,287.

Patented July 31,1906.

means for short-circuitin the armature on said line when the motor is upto speed, and connections for short-circuiting the armaturein a secondline at an angle to the first. The short circuit on the second line maybe closed at starting and may be arranged on the line of field manetization, so as to compensate for the self-induction of thefieldwinding at starting.

When the motor is up to speed and the armature is short-circuited on twolines displaced from each other, it acts as the rotor of a single-phaseinductionmotor, and the motor operates substantially at synchronismunder all loads.

My invention will best be understood by reference to the followingdrawings, in which Figure 1 shows diagrammatically a motor provided witha controlling-switch arranged and connected in accordance with myinvention, and Fig. 2 shows a modification of the same.

In Fig.1, represents the field-winding,

a.Gramme ring. It will be understood, however, that my invention isapplicable to a motor having-any well-known type of winding on bothmembers. A represents the armature, which is "also illustrated a Grammewhich for the sake of simplicity is shown as ring.- Thecommutator-brushes b b, displaced approximately ninety degrees from theline of field magnetization, are connected in series with the field inthe usual manner. A second set of brushes 1) b short-circuit thearmature-winding on the line of magnetiza' tion of the field-winding forthe purpose that has been heretofore explained. \Vith these connectionsthe motor starts as a compensated series motor. S represents a switchwhich when closed short-circuits the commutator-brushes b b. Thus whenthe motor is up to speed and the switch S is closed the armature will beshort-circuited on two lines at an angle to each other, and willconsequently act as the rotor of an ordinary single-phaseinduction-motor.

If the motor is designed for operation on a high-voltage circuit, thearmature-winding may be connected in series with the fieldwindingthrough atransformer instead of directly. Furthermore, otherarrangements of the commutator-brushes may be employed, the'onlyrequirement being that at the start current is supplied to the armatureon a line displaced approximately ninety degrees from the line of tieldmagnetization, while the armature is short-circuitcd on the line oftield magnetization. and when the motor up to speed a short circuit isestablished on the. line on which current was supplied at the startMoreover. the armature need not be directly short-circuited, but mayhave its circuit closed through an impedance or source of compensatingelectromotive force. Thus in Fig. 2 I have shown the armature connectedin series with the tield through a transformer 'l. instead of directly,and a ditlerent arrangement of brushes is employed from that shown inFig. 1. Two pairs of brushes 1) b and I) I) both short-circuit thearmature winding on the line of magnetization of the tield\\'inding. andsince these pairs of brushes are used as the terminals of the armaturefor supplying current to the armature at starting the same results areobtained as in Fig. l.

The switch 3 is arranged to slant-circuit the two sets of brushes uponeach other through the impedance or source of counter electromotiveforce (indicated bys) when the motor is up to speed. At starting theswitch S is opened and the starting current and torque may be controlledby varying the ratio of transformation of the series transformer 'l,

as indicated in the drawings. The motor then starts as a compensatedseries motor.

\Vhen the motor is up to speed, the switch S is closed, and four pointsof the armature winding are then shor't-circuited on each other. Thearmature then acts as the rotor of a singlephase induction-motor, andthe motor operates at substantially synchronous speed. Instead of themanually-operated switch shown in the drawings any suitable type ofautomatic switchsuch, for instance,

as those disclosed inmy former applications may be employed, if desired.

Obviously the motor as described above could be started as a simpleseries motor and the short circuits on both lines produced when themotor is up to speed; but by leaving the brushes 1) b short-circuitedatithc start the power factor of the motor is improved and the switchconnections-are simpler. I desire it to be understood, however, that Ido not.limit myself to a. permanent short circuit on theline oftieldmagnetization, but I intend to cover an arrangement of brushes adaptedto produce the short circuit l whether the. connection between the shrtcircuiting brushes is permanent or not. .\ccordingly, l do not desireto limit myself to the particular construct ion and arrangement of partshcre shown. but aim in the appended claims to cover all modificati nswhich are within the scope of my invention.

hat 1 claim as new. and desire to secure h) Letters Patent ol' thel'nitcd htates. is-- I. in an alternating-currcnt motor, :1 heldwinding.an armatnre-wimlingprovided with a commutator and brushes. connectionsfor supplying current t the armattire-winding on a line at an angle tothe licld magnetization t start the m tor. means F r hort-cir-' cuitingthe armature on said line when the motor is up to speed. and connectionsFor shortircuiting the armature n a second line at an angle to thelirst.

3. ln an alternating-currcnt Itlotona heldwinding. an armaturcovindingprovided with a commutator and brushes. connection f r supplying currentt the artnattii'c \\'iinling in series with the lield n a line at anangl to thc tield magnetization to tart the motor. means forshort-wircuiting the armature on said line when the motor is up to pcch.and connect ions for short-circuit ing the armat are on a second line atan angle t the lirst.

3. in an alternating-currcnt motor. a fieldwinding, anarmatnrewindingprovided with a commutator. brushes arranged to shot!-circuit the armature on the line of lield magnetization, means forsupplying current to the armature-winding on a line at an angle to theticld magnetization, and mean for shortcircuiting the armature on thelatter line when the motor is up to speed.

4. In analternatingcurrent motor, a ticld winding, an atanaturenvinilingprovided with a commutator. brushes arranged to sl1ol't-l'ir cuit thearmature on the line of tield magnetization, means for supplyin currentto t he armature-winding in series with the tield on a line at an angleto the lield magnet ation. and means for sh at'-circuiting the .matureon the latter line when the motor is up to speed.

In witness whereof I have her-cunt.) set my hand this 30th day ofDecember, 1904.

V MAURICE \ll'litll.

'itnesses:

BENJAMIN B. lIt LL, HELEN OaFoan.

